Device for displaying an energy variation and an energy variation bound of an aircraft

ABSTRACT

A display device for displaying information relative to a flight by an aircraft is provided. The information includes information relative to an energy variation of the aircraft, the energy variation being expressed by a variable representative of that energy variation. The display device is configured to show, on a viewing screen, an energy variation symbol representative of a current value of the variable. The display device is configured to further show at least one energy variation bound symbol representative of a threshold value of the variable, the threshold value corresponding to an authorized acceleration bound for the aircraft to keep or bring the speed of the aircraft in or toward a predefined usage speed range.

This is a divisional application of U.S. patent application Ser. No.15/064,502 filed Mar. 8, 2016, which claims the benefit of French PatentApplication FR 15 00533, filed Mar. 18, 2015, which are both herebyincorporated by reference herein.

The present invention relates to a device for displaying informationrelative to a flight by an aircraft, said information comprisinginformation relative to an energy variation of the aircraft, said energyvariation being expressed by a variable representative of that energyvariation, said display device being configured to show, on a viewingscreen, an energy variation symbol representative of a current value ofsaid variable.

The invention in particular aims to assist pilot during piloting inmanual mode, so as to keep the speed of the aircraft in a given speedrange, for example to keep the speed of the aircraft below a maximumauthorized speed, corresponding to a structural limit of the aircraft,and above a minimum authorized speed, associated with an aerodynamicstall incidence of the aircraft.

BACKGROUND

In order to keep the speed of an aircraft in such a speed range, it isknown to provide the aircraft with a protection system configured tolimit the angle of attack and attitude of the aircraft, in order toavoid reaching the stall speed of the aircraft, and to graduallyintroduce, from a threshold speed, a pull up depth command in order toavoid reaching the structural limit of the aircraft.

Nevertheless, these solutions do not make it possible to protect theaircraft against loss of maneuverability. In particular, at low speeds,the capacity of the aircraft to pull up decreases until it is canceledout. Under such conditions, the pilot no longer has a sufficientmaneuvering margin in terms of angle of attack to increase the loadfactor of the aircraft and quickly modify the trajectory of theaircraft.

Likewise, at high speeds, the capacity of the aircraft to dive decreasesuntil it is canceled out, altering the pilot's maneuvering margin tomodify the trajectory of the aircraft.

To resolve this problem, it has been proposed to equip the aircraft witha speed control system, activated once the speed of the aircraft crossesa predetermined threshold, and configured to enslave the speed of theaircraft by controlling the throttle.

This solution is not fully satisfactory. Indeed, this solution is basedon controlling only the thrust, irrespective of the flight configurationof the aircraft, without intervening on the drag of the aircraft, and istherefore generally not optimal. Furthermore, the implementation of theprotection, which involves going from manual control of the throttle toautomatic control of the throttle, can disrupt the manual piloting ofthe aircraft by the pilot.

Also known from document FR 2,958,033 is a device for displayinginformation relative to a flight configuration of an aircraft,comprising information relative to an energy variation of the aircraftand an energy variation range that can be achieved by said aircraft.This energy variation range depends on the thrust values that can begenerated by the engines of the aircraft and the drag force exerted onthe aircraft depending on the position of the air brakes.

Such a device does not provide the pilot with information relative tothe possibility of exceeding speed limits in light of the currentacceleration of the aircraft.

SUMMARY OF THE INVENTION

An objection of the invention is therefore to provide a device fordisplaying information relative to a flight of an aircraft that makes itpossible to inform the pilot when upper and/or lower predetermined speedlimits risk being exceeded, in order to authorize a reaction by thepilot before these limits are exceeded.

To that end, the invention provides a display device of theaforementioned type, characterized in that it is configured to furthershow at least one energy variation bound symbol representative of athreshold value of said variable, said threshold value corresponding toan authorized acceleration bound for said aircraft to keep or bring thespeed of the aircraft in or toward a predefined usage speed range.

According to other aspects, the display device includes one or more ofthe following features:

-   -   the display device is configured to show said energy variation        symbol in a first position on said viewing screen, and to show        said energy variation bound symbol in a second position on said        viewing screen, the distance between the energy variation symbol        and the energy variation bound symbol being representative of a        deviation between the current value of said variable and said        threshold value of said variable, at least as long as the        current acceleration of the aircraft has not exceeded that        acceleration bound;    -   said variable representative of the energy variation is        homogeneous with a slope of the aircraft;    -   the device is configured to show, on said viewing screen, an        artificial horizon line and a speed vector symbol representing a        speed vector of the aircraft, the distance between said        artificial horizon line and said speed vector symbol being        representative of the current slope of the aircraft, according        to a predetermined scale, and the distance between said        artificial horizon line and said energy variation symbol is        representative of the current value of said variable;    -   the distance between said artificial horizon line and said        energy variation bound symbol is representative of the threshold        value of said variable, at least as long as said current        acceleration has not exceeded said acceleration bound;    -   the device is configured to show said energy variation bound        symbol on the viewing screen only when a deviation between the        current value of said variable and said threshold value of said        variable is below a predetermined deviation threshold;    -   said authorized acceleration bound depends on a deviation        between a bound of said usage speed range and a current speed of        said aircraft;    -   the device is also configured to show a graduated speed scale of        the aircraft, along which a speed symbol is illustrated        indicating the current speed of the aircraft as well as a first        speed bound symbol indicating said bound of said usage speed        range;    -   said usage speed range is a maneuverability range of the        aircraft;    -   the device is also configured to show, along said graduated        speed scale of the aircraft, a second speed bound symbol        indicating an authorized speed limit for the aircraft.

The invention also provides a system for displaying information relativeto a flight of an aircraft, comprising:

-   -   a display device according to the invention,    -   an estimating module configured to determine the current value        of said variable representative of the energy variation,    -   a monitoring module configured to determine the threshold value        of said variable, corresponding to the authorized acceleration        bound for said aircraft.

BRIEF SUMMARY OF THE DRAWINGS

The invention will be better understood in light of the exampleembodiments of the invention that will now be described in reference tothe appended figures, in which:

FIG. 1 diagrammatically illustrates a piloting assistance systemcomprising a display device according to one embodiment of theinvention;

FIG. 2 illustrates an illustration mode by the display device of thesystem of FIG. 1 for displaying information relative to the speed andacceleration of the aircraft;

FIG. 3 shows an alternative illustration by the display device ofinformation relative to the speed and acceleration of the aircraft; and

FIG. 4 is a flowchart illustrating the assistance method implemented bythe system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a piloting assistance system 3 for an aircraft 5 comprisinga display device according to one embodiment of the invention.

The aircraft 5 includes a propulsion system 7, for example a set ofengines able to exert a thrust force on the aircraft 5.

The aircraft 5 further includes devices 9 for modifying the drag forceexerted by the air on the aircraft 5, subsequently called drag modifyingdevices, for example drag control surfaces such as air brakes 11 andspoilers 13.

The air brakes 11 can be actuated between a withdrawn position, in whichthe air brakes 11 do not exert any influence on the drag, and a deployedposition, in which the air brakes 11 increase the drag of the aircraft5.

The spoilers 13 can also be actuated between a withdrawn position, inwhich the spoilers 13 do not exert any influence on the drag, and adeployed position, in which the spoilers 13 increase the drag of theaircraft 5. When the spoilers 13 are deployed, they also decrease thelift of the aircraft 5.

The aircraft 5 also includes devices 17 for modifying the trajectory ofthe aircraft 5, for example an elevator and ailerons.

The aircraft 5 further comprises high lift devices, such as slats andflaps, able to modify the lift of the aircraft 5.

The propulsion system 7, the devices 9 modifying the drag force exertedby the air on the aircraft 5 and the devices 17 modifying the trajectoryof the aircraft 5 form devices for controlling the acceleration of theaircraft.

The configuration of the slats, flaps and control surfaces will bereferred to below as the aerodynamic configuration of the aircraft 5.

The aircraft 5 further includes a plurality of sensors 21 making itpossible to determine the values of flight parameters of the aircraft 5,such as its position, its altitude z, its speed and its accelerationrelative to the air and the ground.

For example, an anemometer or airspeed indicator makes it possible todetermine an indicated airspeed V_(I) of the aircraft 5, which is thespeed of the aircraft 5 relative to the air, coming directly frompressure measurements.

The system 3 is configured to assist the crew of the aircraft 5 duringmanual flight, to keep the speed of the aircraft 5 in a first speedrange.

In the rest of the description, unless otherwise indicated, the “speed”of the aircraft 5 is the indicated airspeed V_(I), and the accelerationwill refer to a variation of the indicated airspeed of the aircraft 5,whether it involves a positive acceleration or negative acceleration,also called deceleration.

Hereinafter, “range”, in particular of a speed or acceleration, willrefer to a speed or acceleration interval defined by at least one boundwith a finite value.

The first speed range for example corresponds to a speed rangeachievable by the aircraft 5.

The first speed range is preferably defined by a maximum speed, denotedV_(max), and a minimum speed, denoted V_(min).

The speed V_(max) for example corresponds to a structural limit of theaircraft 5: it is for example a maximum speed that the aircraft 5 canassume without risk to its structure, denoted VD, decreased by a reducedsafety margin. For example, V_(max)=VD X, where X is approximatelyseveral meters per second, for example 0<X≤20 m/s.

Preferably, the speed V_(max) has a fixed value, in particularindependent of the aerodynamic configuration of the aircraft 5 and theflight phase of the aircraft 5.

The minimum speed V_(min) is for example a stall speed of the aircraft5, increased by a safety margin. The minimum speed V_(min) thuscorresponds to the stall incidence of the aircraft 5, beyond which anaerodynamic stall of the aircraft 5 occurs.

The speed V_(min) depends on the aerodynamic configuration of theaircraft 5, the weight of the aircraft 5 and the load factor of theaircraft 5.

The system 3 is configured to assist the crew of the aircraft 5 duringmanual flight, in order to help the crew keep the speed of the aircraft5 in the first speed range, and if possible in a second speed range.

In general, the second speed range is defined as a usage speed rangedesired for the aircraft 5. The second speed range is comprised in thefirst speed range.

This second speed range is for example a maneuverability range of theaircraft, i.e., a speed range in which the aircraft 5 is considered tobe maneuverable, and outside which the maneuverability of the aircraft 5is reduced.

According to another example, the second speed range is a speed rangeassociated with a flight time constraint, i.e., a speed range making itpossible to ensure that the flight time of the aircraft will indeed becomprised in a given flight time range.

According to another example, the second speed range is a speed rangeassociated with a reduced flight envelope, for example in case ofmechanical failure.

In the rest of the description, it will be considered, as an example,that the second flight range is a maneuverability range of the aircraft.

The second speed range is preferably defined by a maximum usage speed,which in the described example is a maximum maneuverability speed,denoted V_(MMSup), and a minimum usage speed, which in the describedexample is a minimum maneuverability speed, denoted V_(MMInf).

The maximum maneuverability speed V_(MMSup) is a speed up to whichminimal maneuverability of the aircraft 5 is guaranteed.

The maximum maneuverability speed V_(MMSUP) is preferably independent ofthe aerodynamic configuration of the aircraft 5 and the flight phase ofthe aircraft 5.

For example, the maximum maneuverability speed V_(MMSup) is defined as afunction of the speed VD, in particular as the speed VD decreased by anincreased safety margin. Thus, the maximum maneuverability speedV_(MMSup) is always below the maximum speed V_(max).

For example, V_(MMSup)=VD−X′, where X′ is approximately several metersper second, for example 10<X′≤30 m/s.

The minimum maneuverability speed V_(MMInf) is a speed of the aircraftbelow which a minimum maneuverability of the aircraft 5 is guaranteed.

For example, the minimum maneuverability speed V_(MMInf) is proportionalto the speed VS1g, which is the stall speed of the aircraft 5 under aload factor of 1 g. The minimum maneuverability speed V_(MMInf) is thatexpressed by V_(MMInf)=k*VS1g, where k is a proportionality factor. Forexample, 1≤k≤1.2.

Preferably, the proportionality factor k depends on the flight phase ofthe aircraft 5. In particular, k can assume a first value duringtakeoff, and a second value, different from the first value, inparticular greater than the first value, during the rest of the flight.

The minimum maneuverability speed V_(MMInf) is generally higher than theminimum speed

The system 3 comprises a computer 30 and man-machine interface means, inparticular an information display device 34.

The computer 30 includes a processor 40 and a memory 42.

The processor 40 is suitable for executing applications contained in thememory 42, in particular an operating system allowing the traditionaloperation of a computer system.

The memory 42 comprises different memory zones containing softwaremodules able to be executed by the processor 40, and data sets.

In particular, the memory 42 comprises an estimator in the form of anestimating module 48, a monitor in the form of a monitoring module 50and an acceleration controller in the form of an acceleration controlmodule 52.

The estimating module 48 is configured to determine, at each moment, thefirst and second speed ranges.

In particular, the estimating module 48 is configured to determine, ateach moment, the speeds V_(min), V_(max), V_(MMInf) and V_(MMSup).

The estimating module 48 is also configured to determine, at eachmoment, a third speed range, included in the first and second ranges.This third speed range is preferably an operational speed range of theaircraft 5, determined between a lower bound, denoted V_(minOp),corresponding to a minimum operational speed of the aircraft 5, and anupper bound, denoted V_(maxOp), corresponding to the maximum operationalspeed of the aircraft 5.

The minimum operational speed V_(minOp) is greater than the minimummaneuverability speed V_(MMInf). The minimum operational speed V_(minOp)is for example proportional to the speed VS1g, and is expressed byV_(minOp)=k′*VS1g, where k′ is a proportionality factor greater than k.For example, 1.2≤k≤1.5.

Preferably, the proportionality factor k′ depends on the flight phase ofthe aircraft 5. Normally, k′ assumes a first value during takeoff, and asecond value, different from the first value, in particular higher thanthe first value, during the rest of the flight.

The maximum operational speed V_(maxOp) is lower than the maximummaneuverability speed V_(MMSup). The maximum operational speed V_(maxOp)is preferably fixed.

The estimating module 48 is also configured to determine, at eachmoment, a total energy variation of the aircraft 5, homogeneous with aslope of the aircraft 5.

At an altitude z, the aircraft 5 has a total mechanical energyE_(total), sum of its kinetic energy and its potential energy, which canbe expressed by:

E _(totale)=½mV _(sol) ² +mgz  (1)

where m designates the mass of the aircraft 5 and V_(sol) is its groundspeed. The variation of this total energy can be expressed by a totalslope γ^(T), according to the equation:

$\begin{matrix}{\gamma^{T} = {{\frac{1}{{mg}\; V_{sol}}\frac{{dE}_{totale}}{dt}} = {\gamma_{sol} + \frac{{\overset{.}{V}}_{sol}}{g}}}} & (2)\end{matrix}$

where {dot over (V)}_(sol) represents the time drift of the ground speedV_(sol) of the aircraft 5.

This variable γ^(Y), homogeneous with a slope, is thus equal to theground slope γ_(sol) of the aircraft 5 when its ground speed V_(sol)remains constant. A variation in the total slope γ^(T) is thereforereflected by a variation in the ground slope γ_(sol) and/or a variationin the ground acceleration {dot over (V)}sol of the aircraft 5. Thus,the total slope γ^(T) represents a variation of the total energy of theaircraft 5.

Yet the critical speeds defined above are speeds of the aircraft 5relative to the air mass (and not relative to the ground).

The estimating module 48 is thus configured to determine a total energyvariation derived from the aforementioned total slope, calledpseudo-total slope and designated by the symbol γ*.

This variable corresponds to the ground slope which, under currentconditions, leads to a constant conventional speed.

Its expression is deduced from the equations of the flight mechanics,and is expressed by:

$\begin{matrix}{\gamma^{*} = {{\gamma_{sol} + {\frac{\left( \frac{\partial V_{air}}{\partial V} \right)_{z = {cste}}}{1 + {\frac{V_{sol}}{g} \cdot \left( \frac{\partial V_{air}}{\partial V} \right)_{{Vc} = {cste}}}}\frac{\overset{.}{V}}{g}}} = {\gamma_{sol} + {A \cdot \frac{\overset{.}{V}}{g}}}}} & (3)\end{matrix}$

The pseudo-total slope γ* is thus a variable homogeneous with a slope ofthe aircraft 5, and the value of which is representative of theacceleration of the aircraft 5. Indeed, when the acceleration of theaircraft 5 is null, the total pseudo-slope γ* is equal to the groundslope of the aircraft 5, and when the acceleration of the aircraft 5 ispositive or negative, the pseudo-total slope γ* is respectively above orbelow the ground slope of the aircraft 5.

The monitoring module 50 is configured to monitor the speed andacceleration of the aircraft 5, and to activate or deactivate theacceleration control module 52, based on the speed and acceleration ofthe aircraft 5.

In particular, the monitoring module 50 is configured to determine, ateach moment, an authorized acceleration range for the aircraft 5 at thatmoment, and to compare, at each moment, the acceleration of the aircraft5 to the authorized acceleration range. The “authorized accelerationrange” refers to the acceleration range allowed for the aircraft withoutan action modifying this acceleration being required, independently ofthe physical capacities of the aircraft to reach or not reach the boundsof this acceleration range. The authorized acceleration range istherefore not defined by minimum and maximum accelerations that theaircraft is able to achieve, but minimum and maximum accelerationsallowed for the aircraft.

Furthermore, the monitoring module 50 is configured to activate theacceleration control module 52 if the acceleration of the aircraft 5 isnot comprised in the authorized acceleration range, and to deactivatethe acceleration control module 52 if the acceleration of the aircraft 5is comprised in the authorized acceleration range.

The authorized acceleration range is defined at each moment as afunction of the speed of the aircraft 5, in particular as a function ofthe deviation between the speed of the aircraft 5 at that moment and thesecond speed range, which in the described example is themaneuverability range of the aircraft 5.

Thus, the comparison of the acceleration to the authorized accelerationrange makes it possible to detect situations in which, without action bythe pilot, the speed of the aircraft 5 would leave or remain outside themaneuverability range, activate the acceleration control module 52 whensuch situations are detected, and keep the acceleration control module52 activated as long as this risk exceeds a determined threshold.

In particular, a case where the acceleration leaves the authorizedacceleration range corresponds to a situation in which, if no correctiveaction is taken to redirect the acceleration, in light of the reactiontimes of the drag, thrust and trajectory modifying devices, an excursionof the speed of the aircraft 5 outside the maneuverability range will nolonger be able to be avoided.

Preferably, the authorized acceleration range is defined by an upperacceleration bound, denoted Acc_(max), and a lower acceleration bound,denoted Acc_(min).

The upper acceleration bound Acc_(max) corresponds to a maximum allowedacceleration in light of the speed of the aircraft 5, in particular thedeviation between the maximum maneuverability speed V_(MMSup) and thespeed of the aircraft 5.

The monitoring module 50 is configured to determine the upperacceleration bound Acc_(max) at each moment as a function of thedeviation between the maximum maneuverability speed V_(MMSup) asdetermined at that moment by the estimating module 48, and the speed ofthe aircraft 5 at that moment.

In particular, the upper acceleration bound Acc_(max) is a strictlyincreasing function of the deviation between the maximum maneuverabilityspeed V_(MMSup) and the speed of the aircraft 5.

Thus, when the speed of the aircraft 5 approaches the maximummaneuverability speed V_(MMSup), i.e., when the deviation between themaximum maneuverability speed V_(MMSup) and the speed of the aircraft 5decreases, the upper acceleration bound Acc_(max) decreases, which isreflected by an approach of the flight zone in which, without action bythe pilot, in light of the acceleration and the reaction time of theacceleration control devices, an excursion of the speed of the aircraft5 above the maximum maneuverability speed V_(MMSup) will not be able tobe avoided.

Furthermore, the upper acceleration bound Acc_(max) is positive as longas the speed of the aircraft 5 remains below the maximum maneuverabilityspeed V_(MMSup), and becomes negative when the speed of the aircraft 5becomes higher than the maximum maneuverability speed V_(MMSup). Thisreflects the fact that, when the speed of the aircraft 5 is above themaximum maneuverability speed V_(MMSup), only a negative action belowthe upper acceleration bound Acc_(max) makes it possible to bring thespeed toward the maneuverability range.

The upper acceleration bound Acc_(max) is for example proportional tothe deviation between the maximum maneuverability speed V_(MMSup) andthe speed of the aircraft 5, and is then expressed as:

Acc _(max) =K*(V _(MMSup) −V),

where K is a strictly positive proportionality factor. For example, thefactor K is fixed, in particular independent of the aerodynamicconfiguration of the aircraft 5 and the flight phase of the aircraft 5.

Alternatively, the upper acceleration bound Acc_(max) is a nonlinearfunction of the deviation between the maximum maneuverability speedV_(MMSup) and the speed of the aircraft 5.

The lower acceleration bound Acc_(min) corresponds to a minimumauthorized acceleration in light of the speed of the aircraft 5, inparticular the deviation between the speed of the aircraft 5 and theminimum maneuverability speed V_(MMInf).

The monitoring module 50 is configured to determine the loweracceleration bound Acc_(min) at each moment as a function of thedeviation between the minimum maneuverability speed V_(MMInf) asdetermined by the estimating module 48 and the speed of the aircraft 5at that moment.

In particular, the lower acceleration bound Acc_(min) is a strictlydecreasing function of the deviation between the speed of the aircraft 5and the minimum maneuverability speed V_(MMInf).

Thus, when the speed of the aircraft 5 decreases and comes closer to theminimum maneuverability speed V_(MMInf), the deviation between the speedof the aircraft 5 and the minimum maneuverability speed V_(MMInf)decreases, and the lower acceleration bound Acc_(min) increases, whichreflects an approach of the flight zone in which, without action by thepilot, in light of the negative acceleration and the reaction time ofthe acceleration control devices, an excursion of the speed of theaircraft 5 below the minimum maneuverability speed V_(MMInf) will not beable to be avoided.

Furthermore, the lower acceleration bound Acc_(min) is negative as longas the speed of the aircraft 5 remains above the minimum maneuverabilityspeed V_(MMInf), and becomes positive when the speed of the aircraft 5becomes lower than the minimum maneuverability speed V_(MMInf). Indeed,when the speed of the aircraft 5 is below the minimum maneuverabilityspeed V_(MMInf), only a positive acceleration above the loweracceleration bound Acc_(min) makes it possible to bring the speed of theaircraft 5 toward the maneuverability range.

The lower acceleration bound Acc_(min) is for example proportional tothe deviation between the minimum maneuverability speed V_(MMInf) andthe speed of the aircraft 5, and is then expressed as:

Acc _(min) =K′*(V _(MMInf) −V),

where K′ is a positive proportionality factor. For example, the factorK′ is fixed, in particular independent of the aerodynamic configurationof the aircraft 5 and the flight phase of the aircraft 5.

Alternatively, the lower acceleration bound Acc_(min) is a nonlinearfunction of the deviation between the minimum maneuverability speedV_(MMInf) and the speed of the aircraft 5.

The monitoring module 50 is also configured to determine a pseudo-totalslope threshold value γ_(max)* associated with the accelerationAcc_(max), equal to:

$\gamma_{{ma}\; x}^{*} = {\gamma_{sol} + \frac{{Acc}_{{ma}\; x}}{g}}$

and a total pseudo-slope threshold value γ_(min)*associated with theacceleration Acc_(min), equal to:

$\gamma_{\min}^{*} = {\gamma_{sol} + {\frac{{Acc}_{\min}}{g}.}}$

Furthermore, the monitoring module 50 is configured to compare, at eachmoment, the acceleration of the aircraft 5, as determined from sensors21, to the lower Acc_(min) and upper Acc_(max) acceleration bounds.

The monitoring module 50 is further configured to activate theacceleration control module 52 if the acceleration of the aircraft 5 atthat moment is above the upper acceleration bound Acc_(max) or below thelower acceleration bound Acc_(min).

The monitoring module 50 is also configured to deactivate theacceleration control module 52 if the acceleration of the aircraft 5 atthat moment is below the upper acceleration bound Acc_(max) and abovethe lower acceleration bound Acc_(min).

The monitoring module 50 is also configured to compare the speed of theaircraft 5 at each moment to the third speed range, in order todetermine whether the speed of the aircraft 5 is comprised in theoperational speed range of the aircraft 5, and to generate an alert,intended for the crew, if the speed at that moment is above the maximumoperational speed V_(maxOp) or below the minimum operational speedV_(minOp).

Preferably, this alert is only emitted if the absolute value of thedeviation between the speed of the aircraft 5 and the maximum or minimumoperational speed is above a given threshold, corresponding to anallowance margin, and if the speed of the aircraft 5 remains outside thethird speed range for a duration exceeding a predetermined length oftime.

This alert is for example emitted by the man-machine interface means 32.This alert is for example an audio and/or visual alert.

The monitoring module 50 is thus configured to generate an alert whenthe speed of the aircraft 5 leaves the operational speed range,therefore before the speed leaves the maneuverability range. Such analert thus gives the crew the opportunity to act on the manual controlsof the aircraft 5 so that the speed of the aircraft 5 returns to theoperational speed range, or at least remains in the maneuverabilityrange.

The acceleration control module 52 can be switched between an activatedstate and a deactivated state. The acceleration control module 52 isable to be activated and deactivated by the monitoring module 50.

In the activated state, in particular when the acceleration controlmodule 52 goes from the deactivated state to the activated state, theacceleration control module 52 is configured to generate an alarm signalintended for the crew. This alarm signal is intended to warn the crewthat an action will be performed by the acceleration control module 52in order to help the crew keep the speed of the aircraft 5 in themaneuverability range.

The acceleration control module 52 is also configured to generate acontrol signal of at least one acceleration control device of theaircraft 5, at least at one control moment, in order to keep or bringthe speed of the aircraft 5 in or toward the usage speed range.

In particular, the acceleration control module 52 is configured togenerate a control signal of the propulsion system 7, in order to modifythe thrust of the aircraft 5, and/or a control signal of the devices 9modifying the drag, in particular the air brakes 11 and spoilers 13,and/or devices 17 modifying the trajectory of the aircraft 5.

In particular, the acceleration control module 52 is configured togenerate a control signal of a first type when the speed of the aircraft5 at the control moment is comprised in the maneuverability range. Thecontrol signal of the first type is preferably a control signal of adevice modifying the drag or thrust of the aircraft 5.

In particular, when the acceleration of the aircraft 5 exceeds the upperacceleration bound Acc_(max), the acceleration control module 52 isconfigured first to generate a control signal for the thrust of theaircraft 5, designed to reduce the thrust of the aircraft 5. Then, ifthe acceleration control module remains active despite this action,i.e., if the acceleration of the aircraft 5 remains above the upperacceleration bound Acc_(max), the acceleration control module 52 isconfigured to generate a control signal of the drag modifying devices 9,in particular an output signal of the air brakes 11 and/or spoilers 13,in order to increase the drag of the aircraft 5.

Conversely, when the acceleration of the aircraft 5 becomes below thelower acceleration bound Acc_(min), the acceleration control module 52is configured first generate a control signal of the drag modifyingdevices 9, in particular a signal to withdraw the air brakes 11 and/orspoilers 13, in order to decrease the drag of the aircraft 5. Then, ifthe acceleration control module 52 remains activated despite thisaction, i.e., if the acceleration of the aircraft remains below thelower acceleration bound Acc_(min), the acceleration control module 52is configured to generate a control signal for the thrust of theaircraft 5, designed to increase the thrust of the aircraft 5.

The acceleration control module 52 is further configured to generate acontrol signal of a second type, different from the first type, when thespeed of the aircraft 5 at the control moment is comprised in the speedrange achievable by the aircraft 5 but not comprised in themaneuverability range. The control signal of the second type ispreferably a control signal of a device modifying the trajectory of theaircraft 5.

Preferably, when the speed of the aircraft 5 at the control moment iscomprised in the speed range achievable by the aircraft 5 but notcomprised in the maneuverability range, the acceleration control module52 is also configured to generate a control signal of the first type, inparticular in order to maintain control of the thrust and drag of theaircraft, or to generate an additional control signal for the thrust ordrag of the aircraft.

For example, when the acceleration of the aircraft 5 is below the loweracceleration bound Acc_(min) and the speed of the aircraft 5 is notcomprised in the maneuverability range, the acceleration control module52 is configured to prevent deployment of the air brakes 11 and/orspoilers 13, which would increase the drag of the aircraft 5, and toprevent a decrease in the thrust of the aircraft 5.

Conversely, when the acceleration of the aircraft 5 is above the upperacceleration bound Acc_(max) and the speed of the aircraft 5 is notcomprised in the maneuverability range, the acceleration control module52 is configured to prevent a withdrawal of the air brakes 11 and/or thespoilers 13, which would decrease the drag of the aircraft 5, and toprevent an increase in the thrust of the aircraft 5.

Thus, when the acceleration of the aircraft 5 leaves the authorizedacceleration range, the acceleration control module 52 is configured togenerate an alarm signal for the crew, then act on the thrust and/ordrag of the aircraft 5 as long as the speed of the aircraft 5 remains inthe maneuverability range, then to act on the trajectory of the aircraft5 if the speed of the aircraft 5 leaves the maneuverability range.

Furthermore, at high speeds, the acceleration control module 52 isconfigured to act on the thrust before acting on the drag, whereas atlow speeds, the acceleration control module 52 is configured to act onthe drag, before acting on the thrust. This sequencing makes it possibleto optimize the influence of the drag and thrust modifying devices.

In the deactivated state, the acceleration control module 52 isdisconnected from any acceleration control device of the aircraft 5 andtherefore does not exert any action on these devices. Thus, when theacceleration of the aircraft 5 leaves the authorized range in light ofits speed, the acceleration control module 52 is configured to modifythe acceleration of the aircraft 5 until the acceleration of theaircraft 5 is once again comprised in the authorized range. Theacceleration control module 52 is then deactivated, and only the manualpiloting commands of the aircraft 5 affect the acceleration controldevices of the aircraft 5.

Thus, when the acceleration of the aircraft 5 is below the loweracceleration bound Acc_(min), the control signals generated by theacceleration control module 52 are designed only to increase theacceleration of the aircraft 5, but in no case to decrease thatacceleration. Likewise, when the acceleration of the aircraft 5 is abovethe upper acceleration bound Acc_(max), the control signals generated bythe acceleration control module 52 are intended only to decrease theacceleration of the aircraft 5, but in no case to increase thatacceleration. In other words, the acceleration control module 52 is notconfigured to regulate the speed and acceleration of the aircraft 5, butonly to provide periodic assistance in order to prevent the speed of theaircraft 5 from leaving the maneuverability range, and to prevent thespeed of the aircraft 5 from leaving the speed range achievable by theaircraft 5.

The information display device 34 in particular comprises a head-upviewing device and a head-down viewing device.

The information display device 34 is configured to display, for thecrew, information relative to the flight of the aircraft 5 during aflight of the aircraft 5.

In particular, the information display device 34 is configured todisplay information representative of the current acceleration of theaircraft 5 and the authorized acceleration range for the aircraft 5. Inparticular, the information display device 34 is configured to show, ateach moment, a symbol representative of the total energy variationassociated with the acceleration of the aircraft 5 at that moment, andto show, at least at some moments, an energy variation bound symbolrepresentative of an energy variation threshold value associated withthe upper bound Acc_(max) or the lower bound Acc_(min) for acceleration.

Such a display allows the crew to view the energy variation margin, inparticular for acceleration, still available for the aircraft 5, and, ifapplicable, to inform the crew when the acceleration of the aircraft 5leaves the authorized acceleration range.

Preferably, the information display device 34 is configured to show anupper energy variation bound symbol, representative of an energyvariation threshold value associated with the upper acceleration bound,only when the deviation between the upper acceleration bound and thecurrent acceleration bound is below a predetermined threshold deviation,i.e., when the current acceleration of the aircraft 5 approaches orexceeds the upper acceleration bound Acc_(max).

Likewise, the information display device 34 is configured to show alower energy variation bound symbol, representative of an energyvariation threshold value associated with the lower acceleration bound,only when the deviation between the current acceleration and the loweracceleration bound Acc_(min) is below a predetermined threshold value,i.e., when the current acceleration of the aircraft 5 approaches orexceeds the lower acceleration bound Acc_(min).

Thus, an energy variation bound symbol is only displayed when theacceleration of the aircraft 5 is close to or exceeds the upperAcc_(max) or lower Acc_(min) acceleration bound. Thus, the energyvariation bound symbol is only displayed when this information isrelevant, which makes it possible both to avoid overloading theinformation display device 34 and to draw the crew's attention when theacceleration of the aircraft 5 is approaching the upper Acc_(max) orlower Acc_(min) acceleration bound.

Furthermore, the information display device 34 is configured to displayinformation representative of the current state of the aircraft 5 andinformation relative to speed bounds for the aircraft 5, in particularthe first and/or the second speed range.

In particular, the information display device 34 is configured to show agraduated speed scale, along which a speed symbol is illustratedindicating the current speed of the aircraft 5.

The information display device 34 is also configured to show, along thegraduated speed scale, speed bound symbols, in particular the maximumV_(max) and minimum V_(min) speeds of the first speed range and/or themaximum and minimum speeds of the second speed range, in the describedexample the maximum V_(MMSup) and minimum V_(MMInf) maneuverabilityspeed, and/or the maximum V_(maxOp) and minimum V_(minOp) operationalspeeds.

Such a display makes it possible to provide information to the crewabout the maneuvering margins that it has in terms of speed.

Furthermore, the display device 34 is configured to display informationrelative to the actions performed by the acceleration control module 52,in particular to indicate a modification in the drag, thrust and/ortrajectory by the acceleration control module 52. Such a display makesit possible to keep the crew informed and thus to minimize disruptionsto manual piloting.

FIG. 2 shows an example illustration of this information by theinformation display device 34.

The information display device 34 comprises a viewing screen 68dedicated to piloting of the aircraft 5. FIG. 2 thus shows informationprojected on this screen, displayed in the form of symbols.

These symbols in particular include a symbol 70 showing a model of theaircraft 5, occupying a fixed position on the screen, which embodies aninfinite projection of the longitudinal axis of the aircraft 5, and anartificial horizon line 72, at the center of the graduated slope scale74. This artificial horizon line 72 is inclined when the roll angle ofthe aircraft 5 is a non-zero angle, during a turn. A speed vector symbol76 of the aircraft 5 indicates the direction of the speed vector of theaircraft 5.

The vertical deviation between the artificial horizon line 72 and thespeed vector symbol 76 of the aircraft 5 represents the ground slopeγ_(sol) of the aircraft 5.

Furthermore, an energy variation symbol 80 indicates a variation intotal energy of the aircraft 5, expressed by a variable representativeof this total energy variation.

In the illustrated example, the variable representative of the totalenergy variation is homogeneous with a slope of the aircraft 5. Theenergy variation symbol 80 is laterally offset relative to the speedvector symbol 76, the relative position of the energy variation symbol80 relative to the graduated slope scale 74 corresponding to the valueof the variable representative of the total energy variation.

Preferably, the variable representative of the total energy variation isthe pseudo-total slope γ* of the aircraft 5.

Thus, the relative position of the energy variation symbol 80 withrespect to the speed vector symbol 76 indicates the acceleration sign ofthe aircraft 5: a horizontal alignment of the energy variation symbol 80and the speed vector symbol 76 reflects a null acceleration; when theacceleration of the aircraft 5 is negative, i.e., the aircraft 5 isdecelerating, the energy variation symbol 80 is positioned below thespeed vector symbol 76, whereas when the acceleration of the aircraft 5is positive, the energy variation symbol 80 is positioned above thespeed vector symbol 76.

Furthermore, the distance between the energy variation symbol 80 and thespeed vector symbol 76 is representative of the absolute value of theacceleration of the aircraft 5.

For example, as shown in FIG. 2, the energy variation symbol 80 is in achevron shape, comprising a lower segment 80 a and an upper segment 80 bthat are oblique and come together to form a tip 80 c, the position ofwhich along the vertical axis indicates, according to the graduatedslope scale 74, the value of the pseudo-total slope γ* of the aircraft5.

Furthermore, an energy variation bound symbol 84, representative of anenergy variation threshold value associated with the upper accelerationbound Acc_(max) or with the lower acceleration bound Acc_(min) isdisplayed, preferably only when the deviation between the upper boundAcc_(max) and the acceleration or the deviation between the accelerationand the lower acceleration bound is below a predetermined thresholddeviation.

The energy variation bound symbol 84 thus indicates an upper or lowerpseudo-total slope bound associated with the upper acceleration boundAcc_(max) or the lower acceleration bound Acc_(min), respectively, inlight of the current ground slope of the aircraft 5.

Thus, the upper energy variation bound symbol indicates a thresholdpseudo-total slope value γ_(max)* associated with the accelerationAcc_(max) equal to:

$\gamma_{{ma}\; x}^{*} = {\gamma_{sol} + \frac{{Acc}_{{ma}\; x}}{g}}$

Likewise, the lower energy variation bound symbol indicates a thresholdvalue γ_(min)* of pseudo-total slope associated with the accelerationAcc_(min), equal to:

$\gamma_{\min}^{*} = {\gamma_{sol} + \frac{{Acc}_{\min}}{g}}$

The energy variation symbol 80 and the energy variation bound symbol 84are laterally offset relative to the speed vector symbol 76, and alignedvertically.

The distance between the energy variation bound symbol 84 and the speedvector symbol 76 is representative of the absolute value of the upperAcc_(max) or lower Acc_(min) acceleration bound.

Furthermore, the distance between the energy variation symbol 80 and theenergy variation bound symbol 84 is representative of a deviationbetween the current acceleration and the acceleration bound Acc_(min) orAcc_(max), as long as the acceleration bound Acc_(min) or Acc_(max) isnot reached.

Preferably, when the acceleration of the aircraft 5 is greater than theupper bound Acc_(min) or lower than the lower bound Acc_(min), theenergy variation bound symbol 84 remains superimposed on the energyvariation symbol 80. The energy variation bound symbol 84 has a shapecomplementary to that of the energy variation symbol 80. For example, asillustrated in FIG. 2, the upper or lower energy variation bound symbol84 comprises an oblique segment 84 a inclined by the same incline as theupper 80 b or lower 80 a segment, respectively, and the vertical segment84 b.

Alternatively, the symbol 84 can be in the shape of a chevron, similarto the symbol 80. The symbols 80 and 84 are then for example differentcolors.

As long as the acceleration of the aircraft 5 is below the upperacceleration bound Acc_(max), the vertical distance between the symbol84 and the symbol 80 is representative of the deviation between theupper acceleration bound Acc_(max) and the acceleration of the aircraft5.

When the acceleration of the aircraft 5 becomes equal to the upperacceleration bound Acc_(max), the oblique segment 84 a of the symbol 84and the upper segment 80 b of the symbol 80 are superimposed.

Likewise, as long as the acceleration of the aircraft 5 is above thelower acceleration bound Acc_(min), the vertical distance between thesymbol 84 and the symbol 80 is representative of the deviation betweenthe upper acceleration bound Acc_(min) and the acceleration of theaircraft 5.

When the acceleration of the aircraft 5 becomes equal to, then lowerthan the lower acceleration bound Acc_(min), the oblique segment 84 a ofthe symbol 84 and the lower segment 80 a of the symbol 80 aresuperimposed.

A graduated speed scale 90 is also displayed, along which a speed symbol92 is shown indicating the current speed of the aircraft 5.

As shown in FIG. 2, the speed symbol 92 is for example in the shape of apentagon, one of the apices of which points to the graduated speed scale90 and indicates the current value of the speed of the aircraft 5 onthat scale. The speed symbol 92 also forms a frame in which the value ofthe current speed of the aircraft 5 appears, in numerical form.

Preferably, the graduations of the graduated speed scale 90 are movablerelative to the speed symbol 92.

Furthermore, a second acceleration symbol 94, representative of thecurrent acceleration of the aircraft 5, is positioned across from thegraduated speed scale 90.

This symbol 94 is for example in the form of an arrow, which pointsdownward or upward depending on whether the acceleration of the aircraft5 is negative or positive, respectively, and the length of which isrepresentative of the value of the acceleration of the aircraft 5,according to a predetermined scale.

Alternatively, the symbol 94 can assume the form of two parallel dasheswith the same length, this length being representative of the value ofthe acceleration of the aircraft 5, along a predetermined scale.

Preferably, the symbol 94 is colored, the color of the symbol 94depending on the acceleration of the aircraft 5.

For example, the symbol 94 is green as long as the acceleration of theaircraft 5 is comprised in the authorized acceleration range, andbecomes amber when the acceleration of the aircraft 5 leaves theauthorized acceleration range.

Furthermore, the symbol 94 becomes red when the acceleration of theaircraft 5 reaches an upper or lower acceleration bound. The upperacceleration bound is for example defined as a function of the deviationbetween the speed of the aircraft 5 and the maximum speed V_(max), whilethe lower bound is for example defined as a function of deviationbetween the speed of the aircraft 5 and the minimum speed V_(min). Thus,a red color of the symbol 94 indicates a flight zone in which, withoutcorrective action on the acceleration, the speed of the aircraft 5 willleave the achievable speed domain.

Furthermore, stop symbols 95, positioned across from the symbol 94,indicate the upper Acc_(max) and lower Acc_(min) acceleration bounds,respectively. The position of the symbols 95 is representative of thevalue of the upper Acc_(max) and lower Acc_(min) acceleration bounds, onthe same scale as that used for the symbol 94. Thus, if the accelerationsymbol 94 exceeds a stop symbol 95, this reflects an excess of the upperAcc_(max) lower Acc_(min) acceleration bound.

The graduated speed scale 90 is further provided with colored bandsdesigned to indicate the critical speed ranges of the aircraft 5, andforming speed bound symbols indicating the speed bounds V_(min),V_(max), V_(minOp), V_(maxOp), V_(MMSup) and V_(MMInf).

These bands comprise two first bands 98 designed to respectivelyindicate the speed interval comprised between the maximum operationalspeed V_(maxOp) and the maximum maneuverability speed V_(MMSup), on theone hand, and the speed interval comprised between the minimumoperational speed V_(minOp) and the minimum maneuverability speedV_(MMInf) on the other hand. In these speed intervals, the speed of theaircraft 5 remains comprised in the maneuverability range, but isoutside the operational speed range. The bands 98 extend along thegraduated speed scale between the maximum operational speed V_(maxOp)and the maximum maneuverability speed V_(MMSup) on the one hand, andbetween the minimum operational speed V_(minOp) and the minimummaneuverability speed V_(MMInf) on the other hand. The bands 98 are forexample amber-colored. In FIG. 2, only the band 98 indicating the speedinterval comprised between the minimum operational speed V_(minOp) andthe minimum maneuverability speed V_(MMInf) is visible.

Two second bands 100 are also designed to respectively indicate thespeed interval comprised between the maximum maneuverability speedV_(MMSup) and the maximum achievable speed V_(max) on the one hand, andbetween the minimum maneuverability speed V_(MMInf) and the stall speedV_(min) on the other hand. In these speed intervals, the speed of theaircraft 5 is no longer comprised in the minimum maneuverability rangeof the aircraft 5. The bands 100 extend along the graduated speed scalebetween the maximum maneuverability speed V_(MMSup) and the maximumspeed V_(max) on the one hand, and between the minimum maneuverabilityspeed V_(MMInf) and the minimum speed V_(min) on the other hand. Thebands 100 are for example amber-colored. In FIG. 2, only the band 100indicating the speed interval comprised between the minimummaneuverability speed V_(MMInf) and the stall speed V_(min) is visible.

Lastly, two bands 102 indicate speed intervals not achievable for theaircraft 5, i.e., speeds above the maximum speed V_(max) or below theminimum speed V_(min). These are speeds that may not in any case bereached by the aircraft 5. These bands are for example red. In FIG. 2,only the band 102 indicating speeds below the minimum speed V_(min) isshown.

FIG. 3 shows an alternative depiction of information by the informationdisplay device 34.

This alternative differs from it the depiction illustrated in FIG. 2 inthat when the acceleration of the aircraft 5 becomes strictly lower(strictly higher, respectively) than the lower bound Acc_(min) (higherthan the upper bound Acc_(max), respectively), the vertical segment 84 bof the energy variation bound symbol 84 elongates upwardly (downwardly,respectively) relative to the oblique segment 84 a, the elongation ofthe vertical segment 84 b being proportional to the deviation betweenthe value of the lower acceleration bound Acc_(min) and the currentacceleration of the aircraft.

According to another alternative that is not shown, the verticaldistance between the symbol 84 and the symbol 80 is still representativeof the deviation between the upper acceleration bound Acc_(max) and theacceleration of the aircraft 5, respectively the deviation between thelower acceleration bound Acc_(min) and the acceleration of the aircraft5, even when the acceleration of the aircraft 5 becomes higher than theupper acceleration bound Acc_(max), lower than the lower accelerationbound Acc_(min), respectively.

FIG. 4 shows a block diagram of one example embodiment of a pilotingassistance method during a flight by the aircraft 5.

This method comprises a step 120 for monitoring the speed andacceleration of the aircraft 5.

This monitoring step 120 is preferably carried out at each moment duringthe flight of the aircraft 5.

The monitoring step 120 comprises a phase 122 for the determination, bythe estimating module 48, of the first, second and third speed ranges.

In particular, during the phase 122, the estimating module 48 determinesthe minimal speed V_(min), based on the aerodynamic configuration of theaircraft 5, the weight of the aircraft 5 and the load factor of theaircraft 5.

The estimating module 48 also determines the minimum maneuverabilityspeed V_(MMInf), based on the flight phase of the aircraft 5.

Furthermore, the estimating module 48 determines the minimum operationalspeed V_(minOp), based on the flight phase of the aircraft 5 at thatmoment.

The monitoring step 120 further comprises a phase 124 for thedetermination, by the estimating module 48, of an energy variation ofthe aircraft 5, characterized by the pseudo-total slope γ*, from theground slope and the acceleration of the aircraft 5.

The monitoring step 120 further comprises a phase 126 for thedetermination, by the monitoring module 50, of the authorizedacceleration range for the aircraft 5 at that moment, based on the speedof the aircraft 5 at that moment, in particular based on the deviationbetween the speed of the aircraft 5 at that moment and themaneuverability range of the aircraft 5.

During the phase 126, the monitoring module 50 determines the upperacceleration bound Acc_(max) as a function of the deviation between themaximum maneuverability speed V_(MMSup), as determined during phase 122by the estimating module 48, and the speed of the aircraft 5 at thatmoment. Furthermore, the monitoring module 50 determines the loweracceleration bound Acc_(min) as a function of the deviation between theminimum maneuverability speed V_(MMInf) as determined during the phase122 by the estimating module 48 and the speed of the aircraft 5 at thatmoment.

The monitoring step 120 next comprises a comparison phase 130, duringwhich the monitoring module 50 compares the acceleration of the aircraft5 to the authorized acceleration range. In particular, the monitoringmodule 50 compares the acceleration of the aircraft 5 to the lowerAcc_(min) and upper Acc_(max) acceleration bounds determined during thephase 126.

At the end of the phase 130, if the acceleration of the aircraft 5 iscomprised in the authorized acceleration range, i.e., if theacceleration of the aircraft 5 is below the upper acceleration boundAcc_(max) and above the lower acceleration bound Acc_(min), themonitoring module 50 does not activate the acceleration control module52 or deactivates it if it had been previously activated, during a phase132.

If, on the contrary, the acceleration of the aircraft 5 is not comprisedin the authorized acceleration range, i.e., if the acceleration of theaircraft 5 is above the upper acceleration bound Acc_(max) or below thelower acceleration bound Acc_(min), the monitoring module 50 judges thatwithout an action to redirect the acceleration of the aircraft 5, anexcursion of the speed of the aircraft 5 outside the maneuverabilityrange will be inevitable. The monitoring module 50 then activates theacceleration control module 52, during a phase 134.

In parallel, during a phase 136 of step 120, the monitoring module 50compares the speed of the aircraft 5 to the third speed range, in orderto determine whether the speed of the aircraft 5 is comprised in theoperational speed range of the aircraft 5. If the speed of the aircraft5 is outside the third speed range, i.e., if the speed of the aircraft 5is strictly greater than the maximum operational speed V_(maxOp) orstrictly less than the minimum operational speed V_(minOp), themonitoring module 50 generates an alert for the pilot.

Preferably, this alert is only emitted if the absolute value of thedeviation between the speed of the aircraft 5 and the maximum or minimumoperational speed is above a given threshold, corresponding to anallowance margin, and if the speed of the aircraft 5 remains outside thethird speed range for a duration exceeding a predetermined length oftime.

The alert is for example emitted by the man-machine interface means 32.This alert is for example an audio and/or visual alert.

Thus, the monitoring module 50 generates an alert when the speed of theaircraft 5 leaves the operational speed range, therefore before thespeed leaves the maneuverability range, independently of the activationof the acceleration control module 52. Such an alert thus gives the crewthe opportunity to act on the manual controls of the aircraft 5 so thatthe speed of the aircraft 5 returns to the operational speed range, orat least remains in the maneuverability range.

Following the phase 134, i.e., following an activation of theacceleration control module 52 by the monitoring module 50, theacceleration control module 52 carries out a step 140 for generating analarm signal intended for the crew, designed to warn the crew that anaction will be taken by the acceleration control module 52 to modify theacceleration of the aircraft 5 if no action is taken by the crew.

If the acceleration control module 52 remains activated following theemission of this alarm signal, i.e., if no action has been taken by thecrew or if, despite an action that has been taken, the acceleration ofthe aircraft 5 remains outside the authorized acceleration range, theacceleration control module 52 implements a step 146 for generating acontrol signal of at least one device controlling the acceleration ofthe aircraft 5 in order to bring the acceleration of the aircraft 5toward the authorized acceleration range, so that the speed of theaircraft 5 stays within the maneuverability range, and in all cases inthe achievable speed range.

The control signal generated by the acceleration control module 52depends on the speed of the aircraft 5. In particular, as long as thespeed of the aircraft 5 remains in the maneuverability range, theacceleration control module 52 acts on the devices modifying the dragand thrust of the aircraft 5, without acting on the trajectory of theaircraft 5. Conversely, if the speed of the aircraft 5 leaves themaneuverability range, the acceleration control module 52 modifies thetrajectory of the aircraft 5 in order to bring the speed of the aircraft5 toward the maneuverability range, while maintaining control over thedrag and thrust modifying devices of the aircraft 5, in particular tomodify the drag and/or the thrust in order to bring the acceleration ofthe aircraft 5 toward the authorized acceleration range, if such amodification is still possible, and to prevent any modification of thedrag and thrust that would keep the acceleration of the aircraft 5outside the authorized acceleration range.

The generating step 146 thus comprises a phase 150 for comparing thespeed of the aircraft 5 to the maneuverability range of the aircraft 5,i.e., to the minimum V_(MMInf) and maximum V_(MMSup) maneuverabilityspeeds, as determined by the estimating module 48 at that moment.

If the speed of the aircraft 5 is comprised in the maneuverabilityrange, the acceleration control module 52 generates a control signal ina phase 152 for controlling at least one device for modifying the dragand/or thrust of the aircraft 5, in order to keep the speed of theaircraft in the maneuverability range.

Preferably, if the acceleration of the aircraft 5 is above the upperacceleration bound Acc_(max), the acceleration control module 52 firstgenerates, during the first phase 152, a control signal for the thrustof the aircraft 5, in particular a control signal for the propulsionsystem 7, in order to reduce the thrust of the aircraft 5. Then, if theacceleration control module remains active despite this action, i.e., ifthe acceleration of the aircraft 5 remains above the upper accelerationbound Acc_(max), the acceleration control module 52 generates, during asecond phase 152, a control signal of the drag modifying devices 9, inparticular an output signal of the air brakes 11 and/or spoilers 13, inorder to increase the drag of the aircraft 5.

Conversely, if the acceleration of the aircraft 5 is below the loweracceleration bound Acc_(min), the acceleration control module 52 firstgenerates, during a first step 152, a control signal for the dragmodifying devices 9, in particular a signal to withdraw the air brakes11 and/or spoilers 13, in order to decrease the drag of the aircraft 5.Then, if the acceleration control module 52 remains activated despitethis action, i.e., if the acceleration of the aircraft 5 remains belowthe lower acceleration bound Acc_(min), the acceleration control module52 generates, during the second phase 152, a control signal for thethrust of the aircraft, in particular a control signal for thepropulsion system 7, in order to increase the thrust of the aircraft 5.

If, conversely, the speed of the aircraft 5 is not comprised in themaneuverability range, the acceleration control module 52 generates, ina phase 154, a control signal of at least one device modifying thetrajectory of the aircraft 5, in order to bring the speed of theaircraft 5 toward the maneuverability range.

During the phase 154, the acceleration control module 52 also controlsthe thrust and drag of the aircraft.

In particular, if the acceleration of the aircraft 5 is below the loweracceleration bound Acc_(min) and the speed of the aircraft 5 is notcomprised in the maneuverability range, the acceleration control module52 prevents, during the phase 154, a deployment of the air brakes 11and/or the spoilers 13, which would increase the drag of the aircraft 5,and prevents a decrease in the thrust of the aircraft 5.

If the acceleration of the aircraft 5 is above the upper accelerationbound Acc_(max) and the speed of the aircraft 5 is not comprised in themaneuverability range, the acceleration control module 52 then prevents,during the phase 154, a withdrawal of the air brakes 11 and/or spoilers13, which would decrease the drag of the aircraft 5, and prevents anincrease in the thrust of the aircraft 5.

As described above, once the monitoring module 50 detects that theacceleration of the aircraft 5 is again comprised in the authorizedacceleration range, the monitoring module 50 deactivates theacceleration control module 52 in a phase 132. In the deactivated state,the acceleration control module 52 is disconnected from any devicecontrolling the acceleration of the aircraft 5 and therefore no longerexerts any action on these devices.

Thus, when the acceleration of the aircraft 5 leaves the authorizedrange in light of its speed, the acceleration control module 52 modifiesthe acceleration of the aircraft 5 until the acceleration of theaircraft 5 is once again comprised in the authorized range. Theacceleration control module 52 is then deactivated, and only the manualpiloting commands of the aircraft 5 affect the acceleration controldevices of the aircraft 5.

In parallel, the information display device 34 displays, during theflight of the aircraft 5, information relative to the flight of theaircraft 5, in particular relative to the speed and acceleration of theaircraft 5, as illustrated in FIG. 2 or 3.

In particular, before each action performed by the acceleration controlmodule 52, during the phases 152 and 154, the display device 34 displaysa message for the pilot, in order to inform the pilot of the actionabout to be taken.

The piloting assistance system and method thus make it possible toassist the crew during a manual flight, in order to prevent the speed ofthe aircraft 5 from reaching one of the bounds of the second speedrange, in particular from reaching values that may compromise itsmaneuverability or even the integrity of its structure, but withoutentering an automatic mode in which the pilot no longer has control overcertain commands, for example a mode in which the automatic throttle,controlling the thrust of the aircraft automatically, is activated.

In particular, the alarm signal generated once the acceleration of theaircraft 5 leaves the authorized range makes it possible to warn thecrew that an action will be performed by the acceleration control module52, and gives the crew an opportunity to manually modify the drag,thrust or trajectory of the aircraft 5 before an action is performed bythe acceleration control module 52. Furthermore, this alarm signal, aswell as the information displayed by the display device 34 relative tothe actions performed by the acceleration control module 52, makes itpossible to inform the crew when a modification of the acceleration willbe or is being done by the acceleration control module 52, and thereforemakes it possible to make the pilot aware that a protection function isbeing implemented and altering manual piloting.

Furthermore, the implementation of protection by the accelerationcontrol module 52 even before the speed leaves the maneuverability rangemakes it possible to have a certain maneuvering margin, and to modifyfirst the thrust and drag of the aircraft 5, in order to redirect theacceleration of the aircraft 5, while retaining the possibility ofmodifying the trajectory of the aircraft 5 subsequently, if themodification of the thrust and drag proves insufficient. Indeed, whenthe speed of the aircraft 5 reaches the maximum or minimummaneuverability speed, the trajectory of the aircraft 5 can still bemodified.

It must be understood that the embodiments described above are notlimiting.

In particular, in one particular embodiment, the assistance system andmethod are implemented only at high or low speeds. This embodimentcorresponds to the case where one of the bounds of the authorizedacceleration range is infinite.

Furthermore, the display device according to embodiments of theinvention can be implemented independently of the assistance system andmethod.

Furthermore, the second speed range can be a desired speed range for theaircraft other than a maneuverability range of the aircraft. Forexample, the second speed range can be defined based on the flight plan,in particular as a speed range guaranteeing passage of the aircraft bycertain points in predefined time intervals.

What is claimed is:
 1. A system for displaying information relative to aflight of an aircraft, comprising: an estimator configured to determinea current value of a variable representative of an energy variation ofthe aircraft during the flight of the aircraft; a monitor configured todetermine a threshold value of the variable, the threshold valuecorresponding to an authorized longitudinal acceleration bound for theaircraft to keep or bring a longitudinal speed of the aircraft in ortoward a predefined usage speed range; and a display device configuredto show, on a viewing screen, an energy variation symbol representativeof a current value of the variable and at least one energy variationbound symbol representative of the threshold value of the variable. 2.The system as recited in claim 1, wherein the usage speed range is amaneuverability range of the aircraft defined between a maximum usagespeed and a minimum usage speed.
 3. The system as recited in claim 2,wherein the threshold value corresponds to an upper authorizedlongitudinal acceleration bound and the upper acceleration bound is astrictly increasing function of the deviation between the maximum usagespeed of the aircraft and the speed of the aircraft.
 4. The system asrecited in claim 3, wherein the upper acceleration bound is proportionalto the deviation between the maximum usage speed and the speed of theaircraft.
 5. The system as recited in claim 3, wherein the upperacceleration bound is a nonlinear function of the deviation between themaximum usage speed and the speed of the aircraft.
 6. The system asrecited in claim 2, wherein the threshold value corresponds to a lowerauthorized longitudinal acceleration bound and the lower accelerationbound is a strictly decreasing function of the deviation between thespeed of the aircraft and the minimum usage speed of the aircraft. 7.The system as recited in claim 6, wherein the lower acceleration boundis proportional to the deviation between the minimum usage speed and thespeed of the aircraft.
 8. The system as recited in claim 6, wherein thelower acceleration bound is a nonlinear function of the deviationbetween the minimum usage speed and the speed of the aircraft.
 9. Thesystem as recited in claim 1 wherein the variable representative of theenergy variation is homogeneous with a slope of the aircraft.
 10. Thesystem as recited in claim 1 wherein the display device is configured toshow the energy variation bound symbol on the viewing screen only when adeviation between the current value of the variable and the thresholdvalue of the variable is below a predetermined deviation threshold. 11.The system as recited in claim 1, wherein the energy variation boundsymbol comprises an oblique segment and a vertical segment, and whereinthe threshold value corresponds to an upper authorized longitudinalacceleration bound and, when a current acceleration of the aircraftbecomes strictly higher than the upper acceleration bound, the verticalsegment of the energy variation bound symbol elongates relative to theoblique segment, the elongation of the vertical segment beingproportional to the deviation between the value of the upperacceleration bound and the current acceleration of the aircraft; orwherein the threshold value corresponds to a lower authorizedlongitudinal acceleration bound and, when a current acceleration of theaircraft becomes strictly lower than the lower acceleration bound, thevertical segment of the energy variation bound symbol elongates relativeto the oblique segment, the elongation of the vertical segment beingproportional to the deviation between the value of the loweracceleration bound and the current acceleration of the aircraft.
 12. Thesystem as recited in claim 2, wherein the estimator is configured todetermine: a first speed range corresponding to a speed range achievableby the aircraft, the first speed range being defined between a maximumspeed corresponding to a structural limit of the aircraft and a minimumspeed; a second speed range, comprised in the first speed range, thesecond speed range corresponding to the usage speed range; a third speedrange, comprised in the second speed range, the third speed rangecorresponding to an operational speed range of the aircraft and beingdefined between a maximum operational speed and a minimum operationalspeed; and wherein the monitor is configured to compare the speed of theaircraft at, each moment, to the third speed range, in order todetermine whether the speed of the aircraft is comprised in theoperational speed range of the aircraft, and to generate an alert,intended for the crew, if the speed at that moment is above the maximumoperational speed or below the minimum operational speed.
 13. The systemas recited in claim 12, wherein the monitor is configured to generatesaid alert only if the absolute value of the deviation between the speedof the aircraft and the maximum or minimum operational speed is above agiven threshold, corresponding to an allowance margin, and if the speedof the aircraft remains outside the third speed range for a durationexceeding a predetermined length of time.
 14. The system as recited inclaim 2, wherein the maximum usage speed of the aircraft is independentof an aerodynamic configuration of the aircraft and of the flight phaseof the aircraft.
 15. The system as recited in claim 2, wherein theminimum usage speed of the aircraft is proportional to the stall speedof the aircraft under a load factor of 1 g.